GOLDEN ORNAMENT MATERIAL HARDENED BY ALLOYING WITH MINOR COMPONENTS

Abstract: A golden ornament material hardened by alloying pure gold having a purity of 99 % or above with 200-2000 ppm of one or more elements selected from Ca, Be, Ge and B, and, when necessary, 10-500 ppm of one or more elements selected from Mg, Al, Si, Mn, Fe, Co, Ni, Cu, Pd, Ag, In, Sn, Sb, Pb and Bi and/or 10-1000 ppm of one or more rare earth elements including Y based on the total quantity of the resultant mixture.

Description: SPECIFICATION TECHNICAL FIELD The present invention relates to gold materials for accessories which are damaged little by rubbing or scratching, as being highly hard to have a Vickers hardness (Hv) of 100 or more, and which maintain said high hardness independently of time or even after heated by brazing or the like. BACKGROUND ART Heretofore, in general, Au alloys having an elevated Hv of 100 or more have been popularly used to produce accessories such as neck chains, brooches, rings, etc. Such Au alloys include, for example, K14 alloys and K18 alloys comprising pure gold having a purity of 99 % or more and approximately from 25 to 40 % by weight of alloying components such as Ag, Cu and even Ni, Pd, Zn, etc. On the other hand, it is said ideal that the above-mentioned accessories are made of pure gold in view of their color and high-quality appearance. However, pure gold has Hv of about 32 as its ingot, while having Hv of about 80 as its worked wire. Even though such pure gold is worked to have an elevated hardness, the elevated hardness of the thus-worked pure gold is inevitably lowered not only with the lapse of time but also when heated by brazing or the like. For these reasons, pure gold accessories are always soft and are therefore easily scratched. It is extremely difficult to keep the esthetic value of such pure gold accessories for a long period of time, and the practical application of pure gold accessories is limited to only an extremely narrow range at present. US-A-3 667 937 discloses an alloy with 99,7% to 99,95% Au and 0,05% to 0,30% Ca. In addition, JP-A-62-29 0836 teaches to use an alloy of 99,99% Au and 0,0002 to 0,0080% Ge. JP-A-2-170931 discloses an ultrafine gold wire used for gold bumps. Its hardness is not disclosed. JP-A-1-87734 discloses material for an ultrafine gold wire used in heat-sensitive element, is sensor for detecting gas or a bioelectrode. The hardness of the known gold wire is about 50 Hv. DESCRIPTION OF THE INVENTION The subject of the present invention is a hardened gold material for accessories having an Hv of more than 100, being made of pure gold having a purity of 99,95% or more alloyed with from 618 to 734 ppm, relative to the total weight of the resulting gold alloy, of one or more alloying components selected from Ca, Be, Ge and B, and from 161 to 613 ppm, relative to the same, of one or more other alloying components selected from rare earth elements including Y. We, the present inventors have studied, from the above-mentioned viewpoints, so as to elevate the hardness of pure gold accessories without detracting from their high esthetic value mentioned above and, as a result, have found that; when pure gold having a purity of 99,95% or more is alloyed with from 618 to 734 ppm, relaitve to the total wheight of the resulting gold alloy, of one or more alloying components selected from Ca, Be, Ge and B, then the resulting gold alloy can have an elevated Hv of 100 or more, while still maintaining said elevated hardness independently of time or even after heated by brazing or the like, and in addition, since the content of the above-mentioned alloying components is small, the hardened gold alloy can still maintain the color and the high quality of pure gold itself and therefore can be formed into gold accessories capable of maintaining a high esthetic value comparable to that of pure gold accessories for a long period of time, that; when said pure gold is alloyed with said alloying component(s) and also from 161 to 613 ppm, relative to the total weight of the resulting gold alloy, of one or more other alloying components selected from rare earth elements including y, (hereinafter referred to as "workability-improving components"), then the resulting gold alloy can have much more improved plastic workability such as drawing workability and rolling workability. In the present invention, pure gold to be alloyed shall have a purity of 99,95% or more. If gold having a purity of less than 99 % is alloyed, the resulting gold alloy no more has the golden color which pure gold possesses and therefore loses the high-quality appearance of pure gold. If the content of the hardness-improving component(s) is less than 200 ppm, it is impossible to elevate the hardness of the resulting gold alloy to have Hv of 100 or more and is also impossible to prevent the thus-elevated hardness of the gold alloy from being lowered with the lapse of time or when the gold alloy is heated. On the other hand, if said content is more than 2000 ppm, the gold alloy can no more have the color and the high-quality appearance of pure gold itself with the result that the esthetic value of the gold alloy is lowered. If the content of the workability-improving component(s) is is because, if less than 10 ppm, it is impossible to attain the intended effects to improve the plastic workability of the gold alloy. On the other hand, if it is more than 1000 ppm, the color of the gold alloy is noticeably worsened. BEST MODES OF PRACTICING THE INVENTION Next, the gold materials for accessories of the present invention are described concretely by means of their examples. Pure gold having a purity shown in Tables 1 to 6 was melted in an ordinary vacuum melting furnace, to which was/were added alloying component(s) of the amount(s) also shown in Tables 1 to 6. Next, the resulting gold alloy was cast into a columnar ingot having a diameter of 20 mm and a length of 100 mm, and test pieces were cut out of the ingot. The hardness (micro-Vickers hardness under 100 gr) of the test piece was measured. The test piece was chamfered and then introduced into a single-head drawing machine where it was repeatedly drawn by 20 passes to be formed into a wire having a diameter of 0.5 mm. In this way, gold alloy wire samples, Nos.15 and 27 of the present invention and comparative examples 1-14,16 to 26 and 28 to 55 were prepared. As a control, a pure gold wire sample was prepared in the manner as above, except that no alloying component was added. The hardness (micro-Vickers hardness under 100 gr) of each of these wire samples was measured immediately after having been drawn and after having been stored for 6 months. In addition, each wire sample was, immediately after having been drawn, heated at 450°C for 30 minutes and then cooled under the conditions corresponding to those for ordinary brazing, for example, using a soldering alloy of Au:3 wt.%-Si having a melting point of 370°C or a soldering alloy of Au:12 wt.%-Ge having a melting point of 350°C. The hardness of each of the thus heat-treated wire samples was also measured in the same manner as above. In order to evaluate the mechanical strength of each wire sample, the tensile strength of each wire sample was measured immediately after having been drawn. The results obtained are shown in Tables 7 to 10. From the results shown in Tables 1 to 10, it is known that all the gold alloy wire samples of the present invention, Nos. 15 and 27 always had a high hardness, namely, Hv of 100 or more even after being stored or even after being heated, while the hardness of the pure gold wire sample having Hv of less than 100 was noticeably lowered after being stored and after being heated. It is therefore obvious that the stability of the hardness of the gold alloy wire samples of the present invention is significantly higher than that of the pure gold wire sample and that the mechanical strength of the former containing strength-improving component(s) was extremely improved. As mentioned hereinabove, the gold materials for accessories of the present invention are hardly scratched as stably and always having an elevated Hv of 100 or more even after being stored or heated. Moreover, since the content of the alloying components in the gold materials of the present invention is small, the gold materials have, in addition to said high hardness, an esthetic value comparable to the excellent esthetic value of pure gold and maintain said esthetic value for a long period of time due to their high hardness. The gold materials for accessories of the present invention thus have practically useful characteristics.

Claims: A hardened gold material for accessories having an HV of more than 100, being made of pure gold having a purity of 99,95% or more alloyed with from 618 to 734 ppm, relative to the total weight of the resulting gold alloy, of one or more alloying components selected from Ca, Be, Ge and B, and from 161 to 613 ppm, relative to the same, of one or more other alloying components selected from rare earth elements including Y.

Inventors: ISHII TOSHINORI, UCHIYAMA NAOKI, ISHII, TOSHINORI, UCHIYAMA, NAOKI, ISHII, TOSHINORI /SANDA PLANT, UCHIYAMA, NAOKI /SANDA PLANT
Applicants: MITSUBISHI MATERIALS CORP, MITSUBISHI MATERIALS CORPORATION
Application year: 1994
Main classification: C22C5
IPC codes: C22C5, A44C27